A Technical I.T./DevOps Blog
Problem scenario
Docker Hub is a public registry for containers. Does OpenShift support something like this? You know they have the OpenShift Container Registry — but this is private to a given OpenShift instance. Red Hat owns OpenShift. Is there a public registry supported by Red Hat?
Answer
Yes. It is called Quay.io. If you want a brief overview of it,
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Continue reading “Is there a Docker Hub equivalent for OpenShift?”
Problem scenario
You know the kubectl version that is running on your client machine. How do you determine the version that your Kubernetes master node is running?
Solution
From the client machine, run this command: kubectl version | grep Server
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Continue reading “How Do You Find the kubectl Version Your Kubernetes Server Is Running?”
Problem scenario
You copied the kubectl file. You are not sure what the permissions it should have. When you try to execute it, you get “Permission denied”. What should you do?
Solution
We recommend using this (after you change directories to the one that has the kubectl file): sudo chmod 777 kubectl
When you use conjure-up, it makes kubectl have 777 permissions.
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Continue reading “What Should The Permissions of the kubectl File Be on a Linux server?”
Problem scenario
You deployed Apache Mesos. The web UI is having problems. You see the error “Failed to connect to x.x.x.x:5050.” What should you do?
Solution
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Question
In Docker what are possible status values of containers?
Answer
Possible statuses include the following:
created, restarting, running, removing, paused, up, exited, or dead
Sources: 1) https://docs.docker.com/engine/reference/commandline/ps/ (for every one except “up”)
2) https://www.thegeekdiary.com/how-to-list-start-stop-delete-docker-containers/ (for “up”)
The docker create command when used with a Docker image ID will produce a new container in the “Created” state.
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Continue reading “What Are The Different Statuses of Individual Docker Containers?”
Problem scenario
You run a command like this: docker build -t “ricepaper:contint”
But you receive a message such as this:
Emulate Docker CLI using podman. Create /etc/containers/nodocker to quiet msg.
no context directory specified, and no dockerfile specified
How do you resolve this problem?
Solution
Use a space and a period at the end of the command.
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Problem scenario
You want to create a resource in a Kubernetes cluster. What should you do?
Solution
You should install Kubernetes. You will need a proper .yaml file in a directory on a server with kubectl installed and configured. You would then run a “kubectl create” command. See this posting for more information.
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Continue reading “How Do You Create a Resource in Kubernetes?”
Problem scenario
You want to use Helm to manage Kubernetes applications. Helm helps you with packages for changes to Kubernetes (in ways that are similar to yum or apt). Helm uses what are call Charts (.yaml files) that enable you to do more with Kubernetes with less trouble. Helm consists of these two things: a CLI tool and a server component that runs as a pod in a Kubernetes cluster (page 531 of Kubernetes in Action by Luksa).
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Continue reading “How Do You Know if You Have Helm Installed and what Version You Are Using?”
Problem scenario
You want to use Helm to manage Kubernetes applications. Helm helps you with packages for changes to Kubernetes (in ways that are similar to yum or apt). Helm uses what are call Charts (.yaml files) that enable you to do more with Kubernetes with less trouble. Helm consists of these two things: a CLI tool and a server component that runs as a pod in a Kubernetes cluster (page 531 of Kubernetes in Action by Luksa).
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Problem scenario
You want to bypass Docker and configure the cgroups directly. You want new Docker containers to be governed by these customized settings. What should you do?
Solution
You may not want to bypass Docker for your cgroup modifications. You should read about the libcontainers. By default Docker uses libcontainers for granular configuration changes along the lines of modifying cgroups settings.
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